FIGS. 5A and 5B represent a heat pump as is illustrated in the European patent EP 2016349 B1. FIG. 5A shows a heat pump which comprises at first a water evaporator 10 for evaporating water as an operating liquid so as to generate a vapor in an operating vapor line 12 on the output side. The evaporator includes an evaporation space (not shown in FIG. 5A) and is configured to produce in the evaporation space an evaporation pressure of less than 20 hPa, so that the water evaporates in the evaporation space at temperatures below 15° C. The water is advantageously ground water, brine circulating in the ground soil in an unconfined manner or in collector tubes, i.e. water with a certain salt content, river water, lake water or sea water. In accordance with the invention, all types of water, i.e. limy water, lime-free water, saline water or salt-free water, may advantageously be used. The reason for this is that all types of water, i.e. all these “water substances”, exhibit a favorable characteristic of water, namely the fact that water, which is also known under “R 718”, comprises an enthalpy difference ratio of 6, which may be made use of for the heat pump process, which is more than 2 times the typical useful enthalpy difference ratio of, for example, R134a.
The water vapor is fed via the suction line 12 to a compressor/condenser system 14 which comprises a flow machine, such as, for example, a centrifugal compressor, exemplarily in the form of a turbo compressor, which in FIG. 5A is designated by 16. The flow machine is configured to compress the operating vapor to a vapor pressure of at least more than 25 hPa. 25 hPa corresponds to a condensing temperature of about 22° C., which, at least on relatively warm days, may already be a sufficient heating flow temperature for underfloor heating. In order to generate higher flow temperatures, pressures of more than 30 hPa may be generated for the flow machine 16, a pressure of 30 hPa corresponding to a condensing temperature of 24° C., a pressure of 60 hPa corresponding to a condensing temperature of 36° C., and a pressure of 100 hPa corresponding to a condensing temperature of 45° C. Underfloor heating systems are designed to be able to provide, even on very cold days, a sufficient degree of heating using a flow temperature of 45° C.
The flow machine is coupled to a condenser 18 which is configured to condense the compressed operating vapor. By means of condensing, the energy contained in the operating vapor is fed to the condenser 18 in order to be then fed to a heating system via the advance element 20a. The operating fluid flows back to the condenser via the return element 20b. 
In accordance with the invention, it is advantageous to withdraw heat (energy) from the water vapor rich in energy by the cooler heating water directly, the heat (energy) being absorbed by the heating water such that same will heat up. An amount of energy is withdrawn from the vapor such that the same is condensed and also participates in the heating cycle.
This means that an introduction of material into the condenser or heating system takes place, which is regulated by an outlet 22 such that the condenser in its condensing space has a water level which, despite continuously feeding water vapor and, thus, condensate, will usually remain below a maximum level.
As has already been explained, it is advantageous to use an open cycle, i.e. evaporating water, which represents the source of heat, directly without a heat exchanger. Alternatively, the water to be evaporated could, however, also be heated up at first by an external heat source using a heat exchanger. However, it may be kept in mind here that said heat exchanger also entails losses and apparatus complexity.
Additionally, it is advantageous, in order to avoid losses for the second heat exchanger, which up to now is usually present on the condenser side, to use the medium there directly, too, i.e. when taking the example of a house featuring underfloor heating, having the water coming from the evaporator circulate directly in the underfloor heating.
Alternatively, a heat exchanger may be arranged on the condenser side, which is fed by the advance element 20a and comprises the return element 20b, wherein said heat exchanger cools the water in the condenser and thus heats up a separate underfloor heating liquid which will typically be water.
Due to the fact that water is used as the operating medium, and due to the fact that only the evaporated part of the ground water is fed to the flow machine, the degree of purity of the water is not important. The flow machine is, as is the condenser and, perhaps, the directly coupled underfloor heating, usually supplied with distilled water such that, compared to present systems, the system entails reduced servicing. In other words, the system is self-cleaning since the system is usually supplied with distilled water only, which means that the water in the outlet 22 is not polluted.
Additionally, it is to be pointed out that flow machines exhibit the characteristic—similarly to a plane's turbine—of not bringing the compressed medium into contact with problematic substances, such as, for example, oil. Instead, the water vapor is compressed only by the turbine or the turbo compressor, but not brought into contact and, thus, polluted with oil or another medium affecting purity.
When there are no other restricting rules, the distilled water discharged by the outlet may then be easily fed again to the ground water. Alternatively, it may, for example, also be seeped in the garden or in an open area, or it may be fed to a water treatment plant via a channel, if rules call for this.
By the combination of water as an operating medium featuring a useful enthalpy difference ratio which is two times better compared to R134a and the consequently reduced requirements to the system being closed (rather, an open system is advantageous), and by using the flow machine, by means of which the compressing factors that may be used are achieved efficiently and without affecting purity, what is achieved is an efficient and environmentally neutral heat pump process which becomes even more efficient when the water vapor is condensed directly in the condenser, since not a single heat exchanger will be required for the entire heat pump process.
FIG. 5B shows a table for illustrating different pressures and evaporating temperatures associated to said pressures, the result being that, in particular for water as an operating medium, relatively low pressures are to be chosen in the evaporator.
In order to achieve a heat pump of high efficiency, it is important for all the components, i.e. the evaporator, the condenser and the compressor, to be designed to be favorable.
DE 4431887 A1 discloses a heat pump system comprising a light-weight large-volume high-power centrifugal compressor. Vapor leaving a compressor of a second stage comprises a saturation temperature which exceeds the surrounding temperature or that of the cooling water available, thereby allowing heat discharge. The compressed vapor is transferred from the compressor of the second stage to the condenser unit which consists of a packed bed provided within a cooling water spraying means on a top, which is supplied by a water circulation pump. The compressed water vapor rises through the packed bed in the condenser where it is in direct counter-flow contact with the cooling water flowing downwards. The vapor condenses and the latent heat of the condensation which is absorbed by the cooling water is emitted to the atmosphere via the condensate and the cooling water which together are discharged from the system. The condenser is rinsed continuously with non-condensable gases, by means of a vacuum pump via a pipeline.
A condenser in which cooling water is in direct counter-flow contact with the condensing vapor, in which the angle between the direction of cooling water on the one hand and the vapor on the other hand is 180 degrees, is of disadvantage in that condensation is not distributed optimally over the volume of the condenser. Condensation here will usually take place only at the interface between water and vapor, which is defined by the cross-section of the condenser. In order to produce a greater condensing performance, the cross-section of the condenser has to be enlarged, or other parameters may be changed, such as, for example, flow through the condenser, vapor pressure in the condenser, etc., which are all problematic on the one hand and, on the other hand, result in an undesired enlargement of the entire system, in particular with regard to enlarging the condensing cross-section. If, however, on the other hand, the system is not enlarged, the result will be that the entire heat pump including a condenser operating in a counter-flow direction does not achieve a performance coefficient which may be used for certain applications where, however, the situation with regard to space is such that enlarging the system has to be ruled out.